Blood extraction devices having a holder with a cannula and a closed end sleeve of valve rubber surrounding the end of the cannula within the chamber defined by the holder can be used for the extraction of blood from a blood vessel of a patient by inserting the sharpened end of the cannula outside the chamber into a blood vessel and inserting into the holder sampling tubes, for example, in succession, permitting the blood to flow through the cannula into the sampling tubes or allowing a syringe-type instrument to draw blood into a sampling vessel through the cannula.
Blood extraction devices utilizing these principles are known in a variety of configurations. For example, U.S. Pat. No. 3,585,984 discloses a blood extraction device with a holder from which a hollow needle cannula extends with a sharp-edged point. The cannula has, at its opposite end, a closed end elastic hose-like valve rubber tube or sleeve surrounding the cannula with an air gap between the cannula and the hose-like tube. The holder has a dome-like formation extending forwardly in which a thickened head or plug of the valve rubber tube projects. This head forms, in effect, a fixed portion of the valve-rubber sleeve which form-fittingly surrounds and engages the cannula and fictionally bears upon the latter internally and upon the holder externally.
A further blood extraction device is described in DE-C 18 12 742 which utilizes a tubular holder open at one end and which receives a hollow-needle double-pointed cannula whose rear end projects into a holder which also serves as a guide sleeve. While the rear end of the doubly-pointed cannula is surrounded by an elastic valve rubber, the front cannula end projects from the end wall of the holder forwardly and can be inserted into a vein of a patient. The blood passing through the cannula enters a sampling tube which is connected at the open end of the holder to the latter. By pushing together the holder and the sampling tube the rear end of the cannula pierces the bottom of the elastic valve rubber and the elastic stopper of the sampling tube so that the rear end of the cannula projects into the sampling tube. The elastic valve sleeve or rubber tube is compressed in an accordion-like manner. After the blood extraction has been completed and the sampling tube is withdrawn from the holder the hose-like valve rubber tube ultimately reassumes its sealing position closing the rear end of the cannula. The holder can be reduced to a disk, i.e. the guide sleeve can be omitted. In this case, the holder disk is connected with the dome of a cap of the blood sampling tube.
Still another configuration has been shown in DE-U 80 16 927 in which the double cannula is received in a cylindrical housing open at one side and provided with a one-piece external cone. On the external cone, a receiving cone of a holder provided with a sharpened cannula or hollow needle can be mounted so that after assembly the double cannula is formed. With this needle configuration, Luer-lock needles of the type commercially used with syringes and blood extraction or sampling tubes can be connected. Elastic rubber valve members can here closely surround the hollow needle of the holder or adapter. The adapter with its Luer cone can also be connected via special adapters or connectors to, for example, a blood-filled tube.
DE-A 29 03 167 discloses a safety cannula with multiple blood sampling in which an accordion like valve rubber tube surrounds a rear end of a double-pointed cannula with a radial air space or radial play. The valve rubber member here has over its entire length an inner diameter which is greater than the outer diameter of the cannula or hollow needle.
When the elastomeric valve member is too close to the needle, friction between the needle and the valve member is unavoidable (see DE-U 80 16 927) and as a result restoration of the elastomeric member from its accordion-like compacted position to its fully extending starting position may be delayed. In that case, upon changing of the blood sampling tube, the expression of blood drops from the cannula cannot be avoided. In general, therefore, it is desirable to avoid any delays in self-closure of the rear end of the cannula.
The frictional delay can be avoided by providing at the rear end of the needle a sufficient radial spacing of the flexible rubber tube from the needle (compare DE-A 29 03 167 and DE-C 18 12 742).
With these systems, the needle is not frictionally engaged by the hose like member but a problem arises in that the position of the hose like member in the holder or adapter cannot be reliably ensured.
The hose-like member in the blood extraction device in DE-C 18 12 742 is formed at its open end with an engagement shoulder which lies against an internal shoulder of the holder and is retained in this position solely by the friction between the surface of the shoulders. The flexible rubber valve sleeve of DE-A 29 03 167 is provided with an external shoulder at its open end which is seated in an annular groove of the end wall of the holder. Here as well the seating of the valve member tends to be loose or readily loosened upon use and problems can be encountered in the mounting of the hose-like valve member in the annular groove.
A variety of other fastening techniques have been used for the hose-like rubber valve member. For example, a form fitting connection is provided by drawing the valve rubber member over a cylindrical boss at a central region of the cannula in DE-A 37 40 269. In EP-A 0 619 096, the valve rubber hose is drawn over a ball-shaped edge bulge while, by contrast, WO-A 95/16395 teaches that the valve rubber tube can be pressed over a conical shoulder with undercuts and can there be cemented.
Finally, according to EP-A 0 678 279, the valve rubber member can be secured in a circumferential collar of circumferential edge within the holder and secured there by a plastic insert.